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Unformatted text preview: NetID: CS411 Database Systems Spring 2010, Prof. Chang Department of Computer Science University of Illinois at Urbana-Champaign Final Examination May 14, 2010 Time Limit: 180 minutes Print your name and NetID below. In addition, print your NetID in the upper right corner of every page. Name: NetID: Including this cover page, this exam booklet contains 16 pages. Check if you have missing pages. The exam is closed book and closed notes. You are allowed to use scratch papers. No calculators or other electronic devices are permitted. Any form of cheating on the examination will result in a zero grade. Please write your solutions in the spaces provided on the exam. You may use the blank areas and backs of the exam pages for scratch work. Please make your answers clear and succinct; you will lose credit for verbose, convo- luted, or confusing answers. Simplicity does count! Each problem has different weight, as listed below So, plan your time accordingly. You should look through the entire exam before getting started, to plan your strategy. Problem 1 2 3 4 5 6 7 Total Points 22 16 11 10 12 15 14 100 Score Grader 1 NetID: Problem 1 ( 22 points ) Misc. Concepts For each of the following statements, indicate whether it is TRUE or FALSE by circling your choice, and provide an explanation to justify. You will get 2 points for each correct answer with correct explanations, and no penalty (of negative points) for wrong answers . (1) False An E-R diagram will translate uniquely to a relational schema. Explain : It can be translated into different relational schemas, depending on different merging strategies, as well as different subclassing methods. (2) False In an E-R diagram, an entity will translate to a table in the relation model, while a relationship will translate to a join between tables. Explain : A relationship in ER diagram normally would also translate into a table in the relation model. For many-to-one relationships, they can be absorbed into the table for entity. (3) True We can consider relational algebra as a query language. Explain : It is a query language, although it is not declarative (SQL is declarative). (4) False The basic operators in relational algebra are ,,, on , ,- . Explain : on is not a basic operator. Instead, Cartesian product is a basic operator. (5) False In SQL, we can only use aggregate functions where there is a Group-By clause. Explain : We can use aggregate directly in Select clause without a Group-By clause. (6) True In rule-based optimization, a commonly used heuristic rule is to push projection down, to reduce the number of columns early on. Explain : It is true. Another heuristic is to push selection down to reduce the number of tuples....
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